Computer networks includes a vast array of interconnected components or network devices (e.g., routers, switches, firewalls, proxy servers, bridges, etc.) for implementing, and/or enhancing the performance of, the network function of transmitting data between end systems. Many such network devices also include control logic for responding to the changes in network state, such as handling situations where a neighboring interconnected device fails and/or the link connecting the two devices goes down for a period of time. For example, a router having several interfaces can adjust its routing functionality in a failover mode to account for a failed, adjacent router or link connected to a given interface.
As one skilled in the art is readily aware, a variety of network devices can be disposed in the communications path between the routers, switches, hubs, bridges, and other network devices, such as bandwidth management devices, proxy caches, and the like. While such intermediate devices do not alter the essential function of the routers and other network devices, the presence of these intermediate systems does interrupt their view of network state and, therefore, affects any functionality responsive to changes in network state, such as the failover measures employed by a router. For example and with reference to FIG. 1, the presence of intermediate device 30 prevents network device 40, such as a LAN switch, from receiving the same feedback it would have otherwise received when network device 22, or the link associated with it, fails. For example, if network device 22 completely fails, network device 40 does not receive the direct feedback, since intermediate network device 30 remains powered and operational. This circumstance prevents network device 40, or perhaps end systems connected to network device 40, from detecting the failover and implementing failover procedures, if any.
As an illustrative example, a router disposed at the edge of a local area network essentially assumes that it has a route to all the hosts on that network as long as it detects that its interface on to the local area network is accessing an active link. Therefore, in a configuration with redundant routers, it is often important that a router be able to detect when its LAN interface goes down, so that it knows when it has lost any part of the path between it and the local hosts that are attached to the LAN.
In a typical LAN, bridges/switches are the main device between the routers and a host. Generally, as long as the bridge/switch is active, the link between the router and the bridge remains active, guaranteeing that the router has a path to all hosts on the LAN. This guarantee is often achieved by using a multiport bridge/switch and providing at least two routes from the bridge/switch to all hosts. So as long as the router sees its LAN interface is active it can assume that it has a path to the local hosts that will survive any single failure. If the bridge/switch fails, the link to the router goes down and the router stops WAN advertisements of any route to the local hosts. This change causes WAN traffic to use the other router which continues to advertise its route to the local hosts.
As discussed above, the problem introduced by bandwidth management devices, such as the PacketShaper® offered by Packeteer, Inc. of Cupertino, Calif., is that it is often be a transparent device sitting between a bridge/switch and a router. However, if the interface with the bridge goes down, the link between the bandwidth management device and the router stays up, preventing the router from determining that it has lost the path to the local hosts.
In light of the foregoing, a need in the art exists for methods, apparatuses and systems that allow an intermediate network device to mirror network state detected on a first network interface on other connections to which it has access. Embodiments of the present invention substantially fulfill this need.